The Collaborative International Dictionary of English v.0.48:

Countervallation \Coun`ter*val*la"tion\ (-v?l-l?"s??n), n.
   (Fort.)
   See Contravallation.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

20 Moby Thesaurus words for "countervallation":
   barbed wire, contravallation, dike, fences, hedge, hedgerow,
   hoarding, paling, palisade, parapet, railing, rampart,
   retaining wall, stockade, stone wall, trellis, vallation, vallum,
   weir, zigzag fence